pgsql: pg_dump: Include column statistics for index-backed constraints

pg_dump: Include column statistics for index-backed constraints

dumpIndex() emits ALTER INDEX .. SET STATISTICS for per-column
statistics targets, but dumpConstraint() never did. Targets set on the
expression columns of an exclusion constraint's index were silently
lost on dump/restore and pg_upgrade.

The same code can be used in the index and constraint dump code to
generate these ALTER INDEX commands. The logic has been refactored so
that both share a new subroutine in charge of generating all these
custom SET STATISTICS, if any.

Oversight in e4fca461ab6f.

Author: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Andrew Krylosov <krylosov(dot)andrew(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAN4CZFMd9riOuV5LkM+uV=uF-HYp49C8Fh22xWyMxptGLBCZ3A@mail.gmail.com
Backpatch-through: 14

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/fa96254c63005dd8d57f5e7af6eb8eac1b9e19e1

Modified Files
--------------
src/bin/pg_dump/pg_dump.c | 86 ++++++++++++++++++++++------------------
src/bin/pg_dump/t/002_pg_dump.pl | 25 ++++++++++++
2 files changed, 72 insertions(+), 39 deletions(-)